1. Field of the Invention
The present invention belongs to the technical field of electric power supply units and electric power supply controlling methods utilizing a plurality of electric power supply lines.
2. Related Background Art
In an audio amplifier for automobile use, it is known that a voltage of an in-vehicle battery is boosted with a DC-DC converter to increase an audio output as described in Japanese Patent Application Laid-open No. Hei-9-291843.
However, there is a case where a current-carrying capacity of a standard electrical wiring in a vehicle, which is 10 amperes for example, is not enough for an audio amplifier utilizing a DC-DC converter. In this case, it is necessary to use a dedicated wiring 120 having a large current-carrying capacity, such as 20 amperes, as described in FIG. 1. The audio amplifier described in FIG. 1 has a power amplifier unit 110 connected to an in-vehicle battery 1 through a connector 102. The power amplifier unit 110 is provided with: a pair of power amplifiers 111A and 11B; a DC-DC converter circuit 112 supplying a power supply voltage to the power amplifiers 111A and 111B; and an on-off detecting circuit 116 for controlling operations of the power amplifiers 111A and 111B by detecting on-off status of an accessory switch 6. Therefore, it is necessary to install the dedicated wiring 120 for passing a current from the battery 1, in a vehicle, and to use a fuse and a connector capable of being used for a current having a large capacity. Thus, complicated work and special components are needed.